Don't judge a placement test mid-month

Don't judge a placement test mid-month
Burned myself here. Ran an A/B on ad placement, called the winner after 5 days, rolled it out — then RPM 'crashed' the next week.
It wasn't my test. RPM swings hard by day of week and time of month (advertiser budgets reset, Q4 vs Q1 is night and day).
— now I run every placement test minimum 14 days
— compare same weekdays, not random ranges
— ignore the first 48h entirely (cache + learning period)
Give the test time or you'll chase noise. Test it on one page first.